Why there are 2 Train Simulator options when creating giveaway?

free CV if they dont fix it xD
Edit: it is not exactly the same like andy said the first one is only the base game and the dlc are seperate keys like the version on HB the other one has them in the package

The URL containing app/24010 is for the base game, but the base game is no longer sold on its own and instead can only be bought on steam as part of a package. That is why on its page it lists several packages which contain the base game, including the package which has sub/392644 in it's URL

If you bought the game from another site, it may be a key for only the base game, or it could be a package key. If the site doesn't say it is a package deal containing DLC, you should pick the option in the game creation list that contains app/24010 to be safe.

appid may be contained in multiple packages (subid). You can't buy just the base game in steam, so when you visit first link steam shows you possible packages. And link with "sub" refers to one particular package. I'm not sure if there is a package that only consist of one appid, there is too many of them. So, in my opinion:
With https://store.steampowered.com/app/24010 you can give away any version, as it only needs to have base game, does not matter if it has other appids (DLCs) or not (any package listed here). With https://store.steampowered.com/sub/392644/ you must give away only this particular version (only this package).